Clothing hygrometer



N, R, s, HOLMES ET AL 3 ,550,439

Dec. 29, 1970 CLOTHING HYGROMETER 2 Sheets-Sheet 1 Filed Sept. 30, 1968FIG] FIGB

INVENTORS NORMAN RS. HOLLIES JOHN APENOYER, SR.

ATTORNEY Dec. 29, 1970 N. R. s. HOLLIES ET AL. 3,550,439

CLOTHING HYGROMETER Filed Sept. 30, 1968 2 Sheets-Sheet B N itznl @2535O O m Q J 4 3 CYCLING RH.

RUN 2 SUBJECT B HYGROMETER RESISTANCE RUN I SUBJECT A RELATIVE HUMIDITYNORMAN R.S.HOLLIES JOHN A. PENOYER,SR.

30 TIME OF EXPOSURE,MIN.

TEMP. 95F

United States Patent Otfice U.S. Cl. 7373 2 Claims ABSTRACT OF THEDISCLOSURE An electrical device and a method of measuring moisture intextiles and other fibrous materials are disclosed. A manner of makingthe device is described. This device is a clothing hygrometer whichcomprises (1) a plastic film bonded to the textile, (2) an inorganic ororganic hygroscopic metal salt, and (3) an overcoat of high conductivitysuch as evaporated metal films which remain solid to about 212 F. toform the hygrometer electrodes.

The device measures water content about from to 50%, relative to theweight of the measured specimen, and is functional at temperatures aboutfrom 32 to 212 F.

A nonexclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sublicenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

This invention relates to a hygrometer and a method of measuringmoisture content of textiles. More particularly, this invention relatesto a clothing hygrometer which measures moisture content of textiles bymeans of electrical energy. This invention is primarily useful inmeasuring the moisture content of systems involving dynamic flow ofmoisture.

One object of the invention is to provide a device of relatively simpleconstruction for measuring moisture content in garments made fromfibrous materials.

A second object of the invention is to provide a method for determiningmoisture content of fibrous materials, such as cotton textiles.

A third object of the invention is to provide a method of fabrication ofa clothing hygrometer.

A fourth object of the invention is to provide a means for measuringmoisture content of surfaces where humidity tends to form throughcondensation, water being provided from any available source. 7

The invention includes the device for measuring moisture content, themethod of making the device, and a method of using the device mainly asa clothing hygrometer. In general the hygrometer of this invention canbe made by:

(a) impregnating a fibrous specimen with an electrolyte solutioncontaining an organic or inorganic hygroscopic metal salt,

(b) allowing the electrolyte solvent to evaporate,

(c) preparing a thin stencil or protective mask, dimensionally stable toheat, the stencil being the complimentary pattern of the electrodearrangement (described in detail below) selected for the particularapplication,

3,550,439 Patented Dec. 29, 1970 (d) placing the stencil from (c) on thefibrous specimen,

(e) applying a thin thermoplastic film on the masked surface of thefibrous specimen,

(f) heating the assembly under pressures about from 1 to 50 pounds persquare inch to the flow temperature of the plastic film, hencedepositing the plastic film on the fibrous specimen,

(g) separating the mask and unbonded plastic film from the specimen andsubjecting the specimen to a second pressing to promote smoothtransition of the plastic film edges into the fibrous surface,

(h) depositing a thin metallic coating on the hot surface of the plasticcoated areas of the fibrous specimen, and

(i) attaching lead wires to the ends of the metallic coatings whichserve as thin film electrodes.

Alternately, the plastic substance can be applied by other methods thanthat described in (c) above. Thus, it can also be applied by depositinga thin plastic film forming rigid substance on the fibrous specimenthrough the stencil and polymerizing the substance in situ.

The present hygrometer is especially adapted to measure the adsorbed oradsorbed moisture content of electrically nonconducting materialsincluding textiles of cotton, wool, or blends with other fibers, andcellulosic papers. The thermoplastic component can be selected from thegroup of nontacky plastic materials such as polyethylene, polypropylene,polyamide, polyvinyl chloride, polyvinylidene chloride, and cellulosics.Alternately, the plastic substance can be applied as a solution oremulsion of continuous film forming materials for textile and papersystems such as solutions or emulsions of polyacrylates,butadiene-acrylonitriles, butadiene-styrenes, polystyrenes,polyethylenes, polyisobutylenes, polyurethanes, polyvinylidenes,polyvinyl organisols, silicones, fiu orocarbons, polyacrylamides,polyimines, styrene-malonic anhydride copolymers, epoxides, andmelamines.

The hygrometer of this invention is used in conjunction with a standardelectrical resistance meter. The observed resistance is then correlatedwith the moisture content of the fibrous material.

It is known that one can determine moisture content using hygroscopicsalts and an electrode system across which the electrical resistance ismeasured; the resistance being proportional to the moisture content.[Humidity and Moisture, Arnold Wexler (editor) volume 1, Section IIIElectric Hygrometry, Reinhold Publishing Corporation, New York (1965).]

It is also known that moisture content of porous substratespredominantly determines their thermal insulating value, such as inclothing or in building construction insulation. [See Textile Res. J.,1965, Hollies] Before the present invention electric hygrometers had notbeen prepared in a thin, flexible form, such as would be required formeasuring clothing properties on people. However, this invention permitsmeasuring moisture differences from one surface to the other of a singlefabric layer, a feature useful in monitoring dynamic transferconditions, as well as measuring moisture collection in a skin-to-fabricinterface. An advantage of the present device is that it is insensitiveto moderate temperature changes.

Although the importance of water in determining the insulating values ofclothing has been established, its importance in determining subjectivecomfort has been hampered by a lack of means to measure water inclothing layers and between clothing layers, while being worn by people.This invention makes it possible to carry out these measurements.

This clothing hygrometer appears to have a number of uniquecharacteristics which include: (1) sensing moisture present at thesurface of a fabric over broad moisture level ranges, (2) it does notsubstantially alter the moisture transmission process of the system inwhich it is used, (3) it does not substantially alter the mechanicalcharacter of the fabric in which it is installed, and (4) it providesmeans for measuring moisture content in a small region of a large samplewithout isolating the sample.

In order that the invention may be better understood, reference is madeto the following description and to the drawings in which:

FIG. 1 is an enlarged cross section of the device of this invention.

FIG. 2 is a plan view showing one pattern for spacing the electrodeelements of this device and the wires which connect them to a resistancemeter (not shown).

FIG. 3 is a plan view of an alternate arrangement of electrode elements.

FIG. 4 represents graphs of moisture measurements taken by means of thepresent device after the latter was sewn into the backs of the shirtsworn by two volunteer subjects.

Referring to the figures, a thin thermoplastic film 2 is laminated byheat and pressure to the fabric substrate 3 through a non-adheringstencil (not shown) to give the electrode paterns selected (see FIGS. 2and 3). Any arrangement of electrodes is acceptable provided they are(1) in the same plane, and (2) at a constant distance with respect toeach other. Fine copper wires 4 (about A.W.G. 40) are used to connectcommon electrode sections, and to provide connections 5 to theresistance measuring device (not shown).

With specific reference to FIG. 1, fabric substrate 3 is initiallysoaked in a salt solution which, on drying, deposits the salt in and onthe fibers. The fibers, so treated, then become the electricallyconducting element sensitive to moisture content variation. The generalappearance of textiles which have been treated in said manner, and whichcontain the electrically conducting film, has not been changed.

A thin metallic film 1 is evaporated in a known manner over the completeelectrode area, resulting in a continuous conducting layer 2 on thethermoplastic film elements.

A number of electrode arangements and the electrolyte concentrations arepossible which would give an operable device. Nevertheles, electrodelength, electrode separation, and electrolyte concentration should bechosen to give a rasonable resistance variation corelated to themoisture range within which practical application is desired. Generally,the electrode and electrolyte choices should give a device in aresistance range of about 1 to 1x10 ohms.

A preferred use of the invention would be that of using the device as aclothing hygrometer, one which would be useful in such investigations asdetermining comfort factors, and the like.

As an example, a 3% ounce 100% cotton printcloth swatch, approximately 6inches square, was bonded to a polyethylene film, using the stenciltechnique described above, to give two electrode areas /8 inch wide, 3inches long, and /s inch apart. The swatch wassaturated in .001 MolarkcL/aq. solution and air dried. Fine copper wires (about number 50A.W.G.) were attached to the ends of each electrode and connected to aresistance bridge.

This particular hygrometerprepared as above-was calibrated in a standardtextile testing room (70 F. and 65% R.H.). Moisture was added dropwiseand the electrical resistance measured when the water was fullydistributed in the hygrometer. Table I shows the results obtained.

4 TABLE I.CLOTHING HYDROMETER CALIBRATION (.001 M kcl., 3-inchelectrodes, As-inch spacing) Moisture added, percent: Resistance, ohmsl0- USING THE DEVICE AS A CLOTHING HYGROMETER A particular hygrometer ofelectrode design of FIG. 2 with 2-inch long electrodes, and prepared asdescribed above was used in a subjective comfort experiment.

The hygrometer was sewn into a shirt in a manner which would place itnext to the skin, on the back of the subject. The leads of thehygrometer were connected to a resistance meter. The shirt was worn bytwo different subjects in an environment of 95 F. and with varying(cycling) relative humidity. The high temperature together with increasein humidity caused the subjects to sweat, and this moisture wastransferred to the sensing elements of the hygrometer. With each subjectthe sweating rate increased as the humidity was increased from 35% toThe shirt and hygrometer worn by the subject with the lower sweatingrate produced a resistance change from 20,000 ohms to 1,600 ohms. Thesubject with higher sweating rate produced a resistance change from32,000 to 50 ohms. These results reflected the increased sweating withincreased thermal stress of both subjects and the difference in sweatingrate of the two subjects exposed to the same thermal stress.

The top two curves in FIG. 4 represent the resistance meter reading forthe two different subjects. Subject JAP (Run 1) perspired more profuselythan did subject. BBJ (Run 2) hence the lower resistance readings in thecase of the former at the high relative humidity (approx. RH. at the 30minute time interval).

The bottom two curves in FIG. 4 are simply the timerelative humidityrelationship taken by a recording humidistat.

We claim:

1. A method of preparing a clothing hygrometer which measures the flowof electric current between two electrodes secured to a fabric specimensubstrate, said method comprising:

(a) impregnating a fabric specimen with a solution of a hygroscopicmetal salt;

(b) allowing the solvent to evaporate;

(c) applying a thin stencil, dimensionally stable to heat,

to the fabric surface, said stencil being the complimentary pattern ofthe electrode arrangement;

(d) applying a thin, thermoplastic film to the stencilcovered surface ofthe fabric specimen;

(e) heating the assembly under pressure of about from 1 to 50 pounds persquare inch to the fiow temperature of the plastic film to bond portionsof the plastic film to the fabric specimen in a pattern corresponding tothat of the stencil;

(f) separating the stencil and unbonded portions of the plastic filmfrom the fabric specimen, thereby leaving on the fabric surface adeposit of plastic film in the electrode pattern;

(g) submitting the specimen to a second heating and pressing step topromote smooth transition of the plastic film edges into the fabricsurface;

(h) depositing a thin metallic coating on the hot surface of the plasticcoated areas of the fabric specimen; and j (i) attaching lead wires tothe ends of the metallic coatings.

2. A hygrometer for determining the moisture content of fabrics bymeasuring the flow of electric current between spaced electrodes ofpredetermined pattern, said hygrometer comprising:

(a) a fabric substrate to support hygrometer elements for attachment tothe fabric whose moisture content is to be measured;

(b) thin, thermoplastic, spaced coatings bonded to the surface of thefabric substrate, said thermoplastic coatings corresponding in patternto a predetermined electrode pattern;

(0) a thin metallic deposit on the surface of said thermoplasticcoatings, said metallic deposit constituting the electrode;

(d) a hygroscopic metal salt impregnated in said fabric substrate, saidsalt constituting a variably conductive 15 electrolyte between saidelectrodes; and

References Cited UNITED STATES PATENTS 10/1962 Jones 338-35 1/1963 Kohl338-35 RICHARD C. TUEISSER, Primary Examiner E. J. KOCH, AssistantExaminer US. Cl. X.R.

